Fixing sleeve for a spark plug

ABSTRACT

A fixing sleeve ( 2 ) for a spark plug ( 1 ) comprising coolant passages ( 3 ) which are arranged in the wall of the fixing sleeve ( 2 ) and which are oriented substantially in the longitudinal direction of the spark plug, wherein the fixing sleeve ( 2 ) comprises a metallic material whose thermal conductivity is over 60 W/m° C., preferably over 80 W/m° C.

DESCRIPTION

[0001] The present invention concerns a fixing sleeve for a spark plugcomprising coolant passages which are arranged in the wall of the fixingsleeve and which are oriented substantially in the longitudinaldirection of the spark plug.

[0002] The function of a fixing sleeve of the kind is to anchor a sparkplug securely and firmly in the cylinder head. For that purpose in thefront region the fixing sleeve has an enlargement which faces in thedirection of the through passage of the fixing sleeve and in which ascrewthread is provided. The spark plug is screwed into thatscrewthread. Besides the function of securely and firmly anchoring thespark plug the fixing sleeve must also carry away the heat which isproduced when ignition occurs. For that purpose, in the state of the art(FIG. 1) the wall of the fixing sleeve has usually been provided withcoolant passages which extend straight. It was possible for thosestraight coolant passages to be easily produced by means of drilling.Practical experience has shown however that the hitherto usual designconfiguration of the fixing sleeve admittedly ensures a good anchorage,but in regard to the cooling effect which is increasingly required, byvirtue of the continuing rise in output of engines, it scarcely attainsthe values required. Inadequate cooling however results in faster wearof the spark plug.

[0003] U.S. Pat. No. 3,765,384 shows an embodiment of fixing sleeve inwhich, in the region of the screwthread into which the spark plug isscrewed, the coolant passages are widened towards the screwthread. Thatconfiguration thus takes the coolant closer to the spark plug, for thepurposes of better cooling.

[0004] Now, the object of the present invention is to provide a fixingsleeve which ensures a longer service life for the spark plugs, byvirtue of a further improvement in the dissipation of heat.

[0005] In accordance with the invention, that is achieved in that thefixing sleeve comprises a metallic material whose thermal conductivityis over 60 W/m° C., preferably over 80 W/m° C.

[0006] Hitherto the material used for the fixing sleeve was high-alloyedsteel as optimum anchoring of the spark plug was the factor to whichprimary attention was paid. The use of a metallic material with a levelof thermal conductivity which is markedly improved in comparison withsteel admittedly involves a reduction in strength properties. Extensivestudies have shown however that it is possible to arrive at a compromisein which the cooling aspect is taken into account to a greater degree.

[0007] Particularly suitable materials are brass or nickel and alloysformed therewith.

[0008] The continuing rises in engine output levels also result in anincreasing level of stress on an antechamber mounted to the fixingsleeve. It is therefore desirable for that antechamber to be made from anickel-chromium alloy with over 25% chromium, preferably about 30%chromium.

[0009] For cooling the antechamber, it is desirable if the antechamberis surrounded by an annular passage into which the coolant passagesopen.

[0010] A preferred embodiment provides that the coolant passages arebrought closer to the spark plug in the front region of the fixingsleeve, which preferably has a screwthread for screwing in the sparkplug. The coolant passages are thus moved closer to the location atwhich the greatest generation of heat occurs and can accordingly moreefficiently carry the heat away.

[0011] An alternative configuration that the coolant passages haveenlargements which face towards the spark plug in the front region ofthe fixing sleeve. Practical tests have shown that, in spite of theweakening of the front region of the fixing sleeve by virtue of thepresence of the enlargements, there is still sufficient stability forsecurely anchoring the spark plug.

[0012] The weakening in the front region can be avoided by theconfiguration of the coolant passages in the front region of the fixingsleeve being adapted to the contour of the spark plug. It will beappreciated however that adaptation to the contour of the spark plugincreases the manufacturing cost for producing the coolant passages.

[0013] Optimum cooling results are achieved if the remaining wallthickness in the front region of the fixing sleeve between the sparkplug and coolant passages is partly below 5 mm, preferably being aboutbetween 2 and 3 mm.

[0014] Further features and details of the present invention will beapparent from the specific description hereinafter. In the drawing:

[0015]FIG. 1 shows a fixing sleeve in accordance with the state of theart,

[0016]FIG. 2 is a view in longitudinal section of a first alternativeembodiment of a fixing sleeve according to the invention,

[0017]FIG. 3 is a view in cross-section taken along line A-A in FIG. 2,

[0018]FIG. 4 is a view in cross-section taken along line B-B in FIG. 2,

[0019]FIG. 5 is a view in longitudinal section of a second alternativeembodiment of a fixing sleeve according to the invention,

[0020]FIG. 6 is a view in cross-section taken along line C-C in FIG. 5,and

[0021]FIG. 7 is a view in cross-section taken along line D-D in FIG. 5.

[0022] As the Figures show the fixing sleeve 2 serves to anchor a sparkplug 1 in the cylinder head 9. In this case the fixing sleeve 2 isdisposed between the inlet and exhaust valves 8.

[0023] The fixing sleeve 2 is reinforced in its front region 2 a.Provided in that region 2 a is a screwthread 5 into which the spark plug1 is screwed.

[0024] The fixing sleeve 2 is provided with coolant passages 3 forcooling the spark plug 1. The coolant passages 3 extend through the wallof the fixing sleeve 2. In the state of the art as shown in FIG. 1 thosecoolant passages 3 are in the form of straight cylindrical bores. Theylead from a manifold 10 straight to the annular passage 7 whichsurrounds the antechamber 6 arranged in front of the spark plug 1 on thefixing sleeve 2.

[0025] In contrast thereto, in the embodiment illustrated in FIG. 2, thecoolant passages 3 are provided with enlargements 4 in the front region2 a of the fixing sleeve 2. The coolant therefore goes closer to thelocation at which the greatest amount of heat is generated in the frontregion of the spark plug 1.

[0026] The fixing sleeve 2 can be made from brass, a brass alloy,nickel, a nickel alloy or also another metallic material if its thermalconductivity is over 60 W/m° C., preferably over 80 W/m° C. At the sametime it must enjoy sufficient strength for securely anchoring the sparkplug 1. The thermal conductivity of brass and nickel is approximatelythree times as high as the high-alloyed steel which has been usedhitherto, whereas the strength values are only slightly worse. Bettermachinability is a further factor in favour of brass and nickel.

[0027] It will be apparent from FIGS. 3 and 4 that disposed in the wallof the fixing sleeve 2 is a plurality of coolant passages 3 whichsurround the spark plug 1. The only exception is that region in whichthe gas injection conduit 11 and the gas injection valve are arranged.The antechamber 6 is supplied with ignition fluid by way of the gasinjection conduit 11 and the gas injection valve The antechamber 6 whichcan be brazed to the fixing sleeve 2 (FIG. 2) or screwed thereto (FIG.5) comprises a nickel-chromium alloy with about a 30% proportion ofchromium. That alloy makes the antechamber 6 particularlyheat-resistant.

[0028] Besides the different connection between the antechamber and thefixing sleeve FIG. 5 differs from FIG. 2 in that the enlargements 4 arein the form of additional bores. Those additional bores are particularlyeasy to implement from the production process point of view. Once againthe remaining wall thickness is greatly reduced. The enlargements 4approach the spark plug 1 to a spacing of between about 2 and 3 mm.

1. A fixing sleeve for a spark plug comprising coolant passages whichare arranged in the wall of the fixing sleeve and which are orientedsubstantially in the longitudinal direction of the spark plug,characterised in that the fixing sleeve comprises a metallic materialwhose thermal conductivity is over 60 W/m° C.
 2. The fixing sleeveaccording to claim 1, characterised in that the fixing sleeve comprisesa metallic material whose thermal conductivity is over 80 W/m° C.
 3. Thefixing sleeve according to claim 1 characterised in that the fixingsleeve comprises brass or a brass alloy.
 4. The fixing sleeve accordingto claim 1 characterised in that the fixing sleeve comprises nickel or anickel alloy.
 5. The fixing sleeve according to claim 1 characterised inthat mounted to the fixing sleeve is an antechamber which comprises anickel-chromium alloy with over 25% chromium.
 6. The fixing sleeveaccording to claim 5 wherein said nickel-chromium alloy comprises about30% chromium.
 7. The fixing sleeve according to claim 5 characterised inthat the antechamber is surrounded by an annular passage into which thecoolant passages open.
 8. The fixing sleeve according to claim 1characterised in that the coolant passages are brought closer to thespark plug in the front region of the fixing sleeve, which region has ascrewthread for screwing in the spark plug.
 9. The fixing sleeveaccording to claim 8 characterised in that in the front region of thefixing sleeve the coolant passages have enlargements facing towards thespark plug.
 10. The fixing sleeve according to claim 8 characterised inthat the configuration of the coolant passages is adapted to the contourof the spark plug in the front region of the fixing sleeve.
 11. Thefixing sleeve according to claim 8 characterised in that the remainingwall thickness in the front region of the fixing sleeve between thespark plug and coolant passages is partially below 5 mm.
 12. The fixingsleeve according to claim 1 characterised in that a plurality of coolantpassages is arranged around the spark plug.
 13. A cylinder headcharacterised in that at least one fixing sleeve according to claim 1 isarranged therein.